The present invention relates broadly to devices for transmitting mechanical energy and, more particularly, to an apparatus which produces a constant rotary output speed from a variable speed rotary input force and is particularly useful in motor vehicle applications.
In conventional automobiles, trucks and similar motor vehicles, a wide variety of accessory equipment is typically provided, including, for example, power-assisted steering and braking units, air conditioner compressors, engine cooling fans, and electrical generators or alternators for providing electrical power for battery charging. The driving members for the various accessories are conventionally rotatably driven directly from the crank shaft of the vehicle engine, with the power being transmitted generally by a belt. Accordingly, the driving members are subject to a widely varying rotational input driving speed during the course of the ordinary operation of the vehicle, the rotary input speed from the crank shaft typically varying several thousand revolutions per minute.
Because ordinary vehicle driving conditions require frequent periods of engine operation at low, idling speeds thereof, most of these accessory units are necessarily designed for operation at full capacity and/or optimum efficiency at low or idling engine speeds. Therefore, at all greater engine speeds in excess of idling speed, a progressively greater than necessary rotational input speed is transmitted from the engine crank shaft to these accessory units, whereby these units are caused to be operated at high level of RPM and thereof inefficiently, with attendant decreases in available motive engine horsepower and fuel economy, throughout the periods of operation of the vehicle at speeds other than idling speed. In addition to the aforementioned disadvantages of inefficiency, the varying rotational input speeds to these accessories create correspondingly varying physical strains, electrical strains or both, thereon which initially requires particular engineering of the accessories to withstand such strains and ultimately may contribute to or cause the premature failure of the accessories.
These problems were addressed in Payne U.S. Pat. No. 4,541,513, defining an invention of the present applicant. There, a fluid power transmission was provided to receive a variable speed rotary input and to provide a constant speed rotary output. In that device, the housing was rotatable and used a centrifugally actuated valve disposed in the housing which remained closed at rotational speeds of the housing assembly at less than a predetermined optimum speed and provided graduated fluid flow in a fluid circuit to create slippage of the housing assembly about a rotor arrangement to limit increases in the rotational speed of the housing assembly over the optimum speed.
Other attempts to provide constant rotary output from a variable speed rotary input include the approach of Wilder, Jr., in U.S. Pat. No. 2,837,193 which is also based on centrifugal force. There, the vanes of a hydraulic motor were made movable to vary the surface area presented to moving hydraulic fluid and therefore the speed of the motor could be controlled. Proper speed control is difficult with the centrifugal devices due to the mechanically displaceable parts which offer a degree of unreliability under the vibrations experienced in motor vehicle operation.